while($obj = mysql_fetch_object($query_user_result_id))
    $arr[] = $obj;
  while($obj_ = mysql_fetch_object($query_user_cards_result_id))
    $arr_ = $obj_;
  while($obj__ = mysql_fetch_object($query_card_theme_result_id))
    $arr__ = $obj__;

// deve essere tipo
{
    "status":"OK",
    "users":[{
        "name":"Diego",
        "surname":"Stamigni",
        "cards" : [{
            "name" : "stocazzo",
            "type" : "stafessa",
            "theme" : {
                "name" : "porno",
                "path" : "./default/"
            }
        ]}
    }]
}